|Publication number||US7421175 B2|
|Application number||US 10/561,021|
|Publication date||Sep 2, 2008|
|Filing date||Jun 23, 2004|
|Priority date||Jun 25, 2003|
|Also published as||DE602004023716D1, EP1636882A2, EP1636882B1, US20070104438, WO2005002008A2, WO2005002008A3|
|Publication number||10561021, 561021, PCT/2004/2712, PCT/GB/2004/002712, PCT/GB/2004/02712, PCT/GB/4/002712, PCT/GB/4/02712, PCT/GB2004/002712, PCT/GB2004/02712, PCT/GB2004002712, PCT/GB200402712, PCT/GB4/002712, PCT/GB4/02712, PCT/GB4002712, PCT/GB402712, US 7421175 B2, US 7421175B2, US-B2-7421175, US7421175 B2, US7421175B2|
|Inventors||Malcolm Paul Varnham|
|Original Assignee||Spi Lasers Uk Limited|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (14), Referenced by (1), Classifications (13), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present application is a U.S. National Stage filing of Patent Cooperation Treaty (“PCT”) application serial number PCT/GB2004/002712, filed 23 Jun. 2004, which in turn claims priority to United Kingdom (Great Britain) Patent Application Serial Number GB0314817.8, filed in The United Kingdom on 25 Jun. 2003.
This invention relates to an apparatus for providing optical radiation. The invention can take various forms, for example a laser, an optical amplifier, a source of amplified spontaneous emission, or a master oscillator power amplifier. The invention has application for materials processing.
Pulsed NdYAG lasers are widely used in industrial processes such as welding, cutting and marking. Care has to be taken in these processes to ensure that the plasmas generated by the laser does not interfere with the incoming laser pulses. The relatively low pulse repetition rates (6 kHz) at high peak powers that are achievable in a NdYAG laser have led to their wide application in laser machining.
Fibre lasers are increasingly being used for materials processing applications such as welding, cutting and marking. Their advantages include high efficiency, robustness and high beam quality. Examples include femtosecond lasers for multiphoton processing such as the imaging of biological tissues, Q-switched lasers for machining applications, and high-power continuous-wave lasers. Their disadvantage is their relatively low energy storage capacity as compared to NdYAG lasers.
In many applications, fibre lasers need to compete with the more mature diode pumped solid state lasers. In order to do so, much greater optical powers need to be achieved, with high reliability and lower cost.
Fibre lasers are typically longer than diode-pumped solid state lasers, and this leads to non-linear limitations such as Raman scattering becoming problematical. It would be advantageous to have fibre lasers that are shorter.
Fibre lasers are typically pumped with diode lasers in bar or stack form, or by many single-emitter diodes that are combined together. Fibre lasers can be core pumped, in which case the pump radiation is guided by the core of the active fibre, or cladding pumped, in which case the pump radiation is guided by the cladding of the active fibre. The active fibre in a cladding-pumped fibre laser needs to be longer than in a core-pumped fibre laser in order to absorb the pump radiation. This is because there is less interaction between the pump radiation and the core in a cladding pumped fibre laser than in a core-pumped fibre laser. Typically, the length of active fibre needs to be longer by the ratio of the cladding cross-sectional area and the core cross-sectional area in order to absorb the pump radiation and provide the necessary output energy. Cladding pumped fibre lasers that have been described in the prior art have inner claddings that are either rectangular, have flats machined on them, have a shape such as a polygon, or are asymmetric.
U.S. Pat. No. 4,815,079 discloses a cladding pumped fibre having a rectangular cladding and another cladding pumped fibre having a circular cladding with an offset core. These designs increase the coupling of pump radiation guided by the cladding and the fibres core. The fibres do not have the combination of a central core and a uniform cladding diameter, which make them difficult to cleave and couple radiation in connectors.
U.S. Pat. No. 5,533,163 discloses a cladding pumped fibre having an inner cladding in the form of a non-rectangular, convex polygon so that the propagating pump energy is induced to form an essentially uniform radiation field in which the various radiation modes comprising the pump energy are isotropically distributed. The fibres do not have the combination of a central core and a uniform cladding diameter, which make them difficult to cleave and couple radiation in connectors.
U.S. Pat. No. 5,864,645 discloses a circular cladding pumped fibre having at least one flat extending along its length to break circular symmetry and to set up chaotic ray behaviour. Such a fibre can be awkward to cleave, the fibre tending to twist when clamped leading to undesirable angled cleaves.
None of the above mentioned prior art shapes provides high coupling of cladding modes with the core modes whilst also combining a substantially regular geometry with curved outside edges that is suitable for cleaving, incorporating into optical fibre connectors, and coupling radiation from substantially round sources.
An aim of the present invention is to provide an apparatus for providing optical radiation that reduces the above aforementioned problem.
According to a non-limiting embodiment of the present invention, there is provided apparatus for providing optical radiation, which apparatus comprises an optical fibre having core, a first cladding and a second cladding, in which the first cladding has a substantially constant diameter in its cross-section.
A first cladding having a substantially constant diameter makes the fibre more suitable for cleaving. Fibre cleavers clamp fibres with mechanical devices. Fibres not having a constant diameter can twist during this process. Thus a fibre with a substantially constant diameter is advantageous and provides distinct advantages over the prior art.
The first cladding may be non-circular.
The first cladding may have at least one axis of mirror symmetry.
The first cladding may have a geometric centre. The core may be located at the geometric centre. Having a fibre with a core in its geometric centre facilitates coupling of optical radiation in connectors and splices. The core may be offset from the geometric centre which may be advantageous in certain circumstances—for example in coupling to another fibre having an offset core, or for increasing mode coupling in certain fibre geometries.
The core may be centred at the centre of the smallest imaginary circle that can contain the first cladding. Alternatively, the core may be offset from the centre of the largest imaginary circle that can be contained within the first cladding.
The first cladding may comprise circular arcs having centres at the vertices of an equilateral star. The circular arcs may have a first radius equal to the length of the side of the star. The circular arcs may each have a first radius greater than the length of the side of the star, which circular arcs are joined by circular arcs each having a centre located at the vertices, and a second radius equal to the difference between the first radius and the length of the side of the star.
Each line of the star preferably crosses all the other lines of the star. The star may be an equiangular star. Alternatively, the star may contain at least two different angles.
The star preferably contains an odd number of vertices.
The fibre may contain at least one longitudinally extended hole. The hole may be circular. Alternatively, the hole may be non-circular.
The fibre may contain at least one region of low refractive index. The region of low refractive index may be circular. Alternatively, or in addition, the region of low refractive index may be non-circular.
The fibre may comprise rare-earth dopant. The rare earth doping may be selected from the group comprising Ytterbium, Erbium, Neodymium, Praseodymium, Thulium, Samarium, Holmium and Dysprosium, Erbium codoped with Ytterbium, or Neodymium codoped with Ytterbium.
The apparatus may comprise a pump source for providing pump radiation coupled to the first cladding.
The apparatus may be in the form of a laser, an amplifier, a source of amplified spontaneous emission, or a master oscillator power amplifier.
It is preferred in the embodiments described above that the refractive index of the core is greater than the refractive index of the first cladding. It is also preferred that the first cladding has a higher refractive index than the second cladding. The first cladding may be a glass such as a silica, doped silica, or a phosphate glass. The second cladding may be a polymer, silica, a doped silica, a fluorosilicate, or a doped phosphate glass. If the second cladding is a glass, then it is preferred that the second cladding is coated with a polymer.
Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which:
With reference to
By diameter 9 it is meant the diameter or width of the first cladding 1.
It is preferred that the refractive index of the core is greater than the refractive index of the first cladding 1 which has a higher refractive index than the second cladding 2. The first cladding 1 may be a glass such as a silica, doped silica, or a phosphate glass. The second cladding 2 may be a polymer, silica, a doped silica, a fluorosilicate, or a doped phosphate glass. If the second cladding 2 is a glass, then it is preferred that the second cladding 2 is coated with a polymer.
The shape of the first cladding 1 shown in
An advantage of utilizing such a first cladding 1 is illustrated in
Further examples of the first cladding 1 are first claddings 31, 41, 51, 61, 71, 81, 91, and 101 shown in
The stars 32 shown in
The first claddings 91 and 101 shown with reference to
With reference to
Fibres containing a first cladding 1 as described with reference to the above figures can be fabricated by inserting a modified chemical vapour deposition perform into a pre-machined glass capillary having the desired outer contour and materials properties. The machining can be performed using ultrasonic milling and/or lapping.
The laser 180, the amplifier 190, the source of amplified spontaneous emission 200, and the master oscillator power amplifier 210 are believed to have important application as sources of high power laser radiation for industrial and aerospace applications including materials processing. In such applications it is often desirable to synchronise the pump source 182 with the movement of an optical scanner.
It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications and additional components may be provided to enhance performance.
The present invention extends to the above-mentioned features taken in isolation or in any combination.
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|Citing Patent||Filing date||Publication date||Applicant||Title|
|US8947768||May 13, 2013||Feb 3, 2015||Jds Uniphase Corporation||Master oscillator—power amplifier systems|
|U.S. Classification||385/126, 372/6, 385/123, 385/128, 385/146|
|International Classification||H01S3/067, G02B6/02, H01S3/30, G02B6/36|
|Cooperative Classification||H01S3/094007, H01S3/06708, H01S3/06729|
|Dec 16, 2005||AS||Assignment|
Owner name: SPI LASERS UK LIMITED, UNITED KINGDOM
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:VARNHAM, MALCOLM PAUL;REEL/FRAME:017382/0814
Effective date: 20051214
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